1. Technical Field
The present invention relates to a method for removing surfactants, organic materials and chlorine ions existing on the surface of metal nanoparticles which are prepared by using an organic solvent including a surfactant.
2. Description of the Related Art
Korean Patent No. 10-0845688 discloses a method for removing Ni(OH)2 and impurities existing on the surface of nickel particles by using a reductive organic solvent to increase the purity of the metal by removing nickel hydroxides and metal oxides. JP H4-235201 A discloses a method for increasing a tap density of metal powder by adding the metal powder into an organic solvent including a stearic acid and evaporating out the organic solvent from the mixture. Such a conventional method may cause coagulation between particles during the evaporating process of the solvent when the solvent is evaporated by heating. This method is usually effective when nickel hydroxides or nickel oxides are presented on the surface of metal nanoparticles.
The metal nanoparticles, which are prepared on an organic solvent phase including a surfactant, are well dispersed in a non-polar solvent such as toluene and hexane. A polar solvent such as alcohol and acetone is then added into the mixture solution including such well-dispersed nanoparticles, and the nanoparticles are precipitated out as powder by employing a centrifugal separator. However, when this method is used, even though the organic solvent and the surfactant remaining on the surface of the nanoparticles are removed by using alcohol and toluene, organic materials, particularly chlorine ions used as a reactant, can be still remained after such washings. When the organic materials and the chlorine ions are remained on the surface of the nanoparticles, it deteriorates electrode characteristics of a multi layer ceramic capacitor (MLCC) or it may be toxic when they are used for human being products.
Therefore, it is highly demanded to develop a more effective method to remove such chlorine ions in the process of manufacturing metal nanoparticles.